fix(build): apply rewrites when computing createContentLoader urls

URLs were derived from the source path only, so loader-generated links
pointed at the pre-rewrite location and 404ed for rewritten pages.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/node/contentLoader.ts

@@ -131,9 +131,10 @@ export function createContentLoader<T = ContentData[]>(
               : { excerpt: renderExcerpt as any } // gray-matter types are wrong
           )
 
+          const relFile = normalizePath(path.relative(config.srcDir, file))
           const url =
             '/' +
-            normalizePath(path.relative(config.srcDir, file))
+            (config.rewrites.map[relFile] || relFile)
               .replace(/(^|\/)index\.md$/, '$1')
               .replace(/\.md$/, config.cleanUrls ? '' : '.html')